JPS6117536A - Preparation of benzophenonetetracarboxylic acid - Google Patents

Abstract

PURPOSE:To obtain the titled compound useful as a raw material for a polyimide of a heat-resistant material in high purity, by oxidizing bis(dimethylphenyl) ethane with nitric acid with a specific concentration at a specific temperature, recrystallizing the crude reaction product separated by concentration, etc. with water. CONSTITUTION:Bis(dimethylphenyl)ethane shown by the formula I is oxidized 25-40wt%, preferably 28-35wt% nitric acid at 120-170 deg.C, preferably at 125- 165 deg.C, to give benzophenonetetracarboxylic acid(BTA) shown by the formula II. The reaction product solution is concentrated, cooled, or cooled after concentration, to precipitate and to separate crude BTA. Then, crude BTA is recrystallized by the use of water as a solvenet for recrystallization, to give purified BTA. Part or the whole (preferably 50-90wt%) of the mother liquor separated from crude BTA is sent to the oxidation process, 5-25wt% recrystallized mother liquor is replaced with new water, and preferably recycled through the recrystallization process.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method for producing highly pure benzophenone tetracarboxylic acid.

BACKGROUND ART Benzophenonetetracarboxylic acid (hereinafter referred to as "BTAJ") can be made into benzophenonetetracarboxylic dianhydride (hereinafter referred to as "BTDAJ") by dehydration, and this BTDA is a polyimide which is a heat-resistant resin. Particularly useful as a raw material.

Conventionally known methods for producing BTA include a method of oxidizing bis(dimethylphenyl)propionic acid, a method of oxidizing bis(dimethylphenyl)methane, and a method of oxidizing bis(dimethylphenyl)ethane.

In these methods, bis(dimethylphenyl)ethane (dixylinoethane, hereinafter referred to as rDXEJ), which can be easily synthesized from 0-xylene and acetaldehyde, etc.
is used as a raw material and oxidized with nitric acid (DXE oxidation method)
is considered the most practical.

Problems to be Solved by the Invention As the DXE oxidation method, for example, Soviet Patent No. 232
, 237 describes a method of oxidizing at 150 to 200° C. using nitric acid at a low concentration of 10 to 20% by weight.

However, this method uses a large amount of aqueous nitric acid solution with a low concentration of nitric acid, so it has the disadvantage that the efficiency of reactor use is poor and that a large amount of energy is consumed to precipitate crude BTA after the reaction.

On the other hand, according to US Pat. No. 3,671.5879, there is a method of continuous oxidation at around 170°C using high concentration nitric acid of about 70%, and US Pat. No. 4,17
No. 3,573 discloses a method in which nitric acid of 54% by weight is gradually fed and oxidized at a temperature of 140 DEG to 175 DEG C. According to these methods, the nitric acid concentration is high (and the efficiency of the reactor is improved, but on the other hand, the amount of by-products produced increases, and the color of the crude BTA obtained remains yellow even after repeated recrystallization. Even if the obtained BTA is dehydrated and purified to produce BTDA, it will not become white, but a cream-colored BTA.
It becomes TDA.

In fact, the BTDA currently on the market appears to be manufactured using these methods, but it is cream-colored and has a purity of 96%.
It is ~97% powder crystal, and is difficult to become white crystal even if recrystallization is repeated.

In recent years, polyimide has attracted attention as a heat-resistant material, and although there is a demand for high-purity, highly transparent polyimide especially for electronic materials, and for high-purity monomers for that purpose, there is still a lack of BTDA, the monomer of polyimide. Currently, there is no known method for efficiently producing a highly pure white product.

The present invention was made against the background of such technical problems, and
Few by-products (Highly purified BT, the raw material for BTDA)
The purpose of the present invention is to provide a manufacturing method capable of obtaining A.

A means for solving the problem, that is, the present invention is a method for producing benzophenonetetracarboxylic acid, which is characterized by including the following steps.

(a) Bis(dimethylphenyl)ethane at a concentration of 25~
The first step is to carry out an oxidation reaction using 40% by weight of nitric acid at a temperature of 120 to 170°C.

(b) A second step of concentrating or cooling the reaction product liquid, or cooling after concentration to precipitate and separate crude benzophenonetetracarboxylic acid.

(c) A third step of recrystallizing crude benzophenonetetracarboxylic acid using water as a recrystallization solvent.

The present invention will be explained in detail below by dividing it into steps.

(a) First step The first step is, for example, a DXE oxidation reaction shown by the following reaction formula.

+35/3H*O+34/3NO Here, DXE used in the present invention is obtained, for example, by condensing 0-xylene and acetaldehyde,
For example, it may contain a small amount of extractant such as a hydrocarbon used when separating isomers, unreacted 0-xylene, and condensates, but if there are many impurities, the mother liquor after BTA precipitation and separation may be used as described below. Since the amount that can be recycled to the reactor in this process will be correspondingly smaller, it is preferable to use DXE.
The purity is 95% by weight or more.

The concentration of nitric acid used for oxidation is 25 to 40% by weight, preferably 28 to 35% by weight. In the DXE oxidation reaction, when the concentration of nitric acid used exceeds approximately 40% by weight, the production rate of a yellow compound as a by-product increases rapidly; If the nitric acid concentration is too low, a large amount of nitric acid aqueous solution must be used, resulting in poor reactor usage efficiency and a large amount of energy being consumed for concentrating the reaction product solution after the reaction and for precipitating and separating BT and A. Both are necessary and undesirable.

The amount of nitric acid used is preferably 10 to 20 moles in terms of 100% by weight nitric acid per mole of DXE.

The theoretical amount of nitric acid used is 11.33 from the above reaction formula.
If the amount of nitric acid is less than about 10 moles per mole of DXE, the reaction will not proceed sufficiently, while a large amount of nitric acid exceeding about 20 moles is unnecessary and is disadvantageous because it is difficult to handle after the reaction. Become.

Further, the reaction temperature in the above reaction is 120 to 170°C, particularly preferably 125 to 165'C.

In the DXE oxidation method according to the present invention, there is a correlation between the amount of the yellow compound produced as a by-product and the reaction conditions, and the amount of the by-product is greatly influenced by the nitric acid concentration and reaction temperature.

That is, when the reaction temperature is below 50°C, the reaction rate is extremely slow;
If the reaction rate exceeds 50°C and falls below 120°C, the reaction rate gradually increases, but the amount of yellow compounds as by-products increases.
The production rate of the yellow compound sharply decreases when the reaction temperature is higher than .degree. Furthermore, when the reaction temperature exceeds 170°C, the yellow compound produced as a by-product is small, but it is difficult to completely separate the yellow compound even by recrystallization using water in the subsequent step, and the BTA obtained by recrystallization is It is colored and is unlikely to be white. That is, this phenomenon is considered to be because some of the by-products produced under such reaction temperature conditions have a structure very similar to BTA.

Furthermore, if the reaction temperature exceeds 170° C., by-products such as carbon dioxide will increase, and the reaction rate will also increase, making it easy for the reaction to run out of control and making it difficult to control.

Note that the reaction time is usually about 1 to 10 hours. Further, the reaction may be carried out in a closed system or in a pressurized open system. When carried out in a closed system, the pressure changes depending on the filling rate of the raw material liquid due to the generation of carbon dioxide and oxygen and nitrogen. Therefore, the filling rate of the liquid must be determined according to the pressure resistance of the reactor, and when the filling rate at room temperature is about 50%, the pressure during reaction is about 30 to 7017 g/-.

After the reaction is completed, the reaction product liquid obtained is preferably 10 to 5
A pale yellow aqueous solution or suspension is obtained by cooling to about 0° C., releasing gas as necessary, and returning the reaction system to normal pressure.

The unreacted nitric acid in the reaction product solution can be neutralized with an alkaline substance, but as will be described later, such nitric acid can also be recycled into the reaction system, so it is not necessary to neutralize it.

(b) Second step BTA will precipitate even if the reaction product solution obtained is left at room temperature, but it takes a long time to precipitate and the amount of BTA precipitated is small.

Therefore, in the second step, the reaction product liquid is either i) concentrated (concentration method), ii) cooled (cooling method), or +ii
) After concentration and cooling (concentration/cooling method), crude BTA is precipitated and separated from the reaction product liquid.

(i) In the case of the concentration method, BTA is precipitated by boiling the reaction product liquid or boiling it under reduced pressure of about 50 to 500 Torr and distilling off a part of the volatile components.

In addition, ii) When using the cooling method, the reaction product liquid is reduced to 0.
BTA is precipitated by cooling to ~10°C.

Furthermore, iii) in the case of concentration/cooling method, i) and ii
) may be combined.

The concentration of BTA at the time of recrystallization is preferably 10 to 20% by weight, and crude BTA will easily precipitate if allowed to cool at this concentration.

The amount of BTA precipitated is also related to the concentration of nitric acid remaining in the mother liquor, and the higher the nitric acid concentration, the lower the amount of BTA precipitated. Therefore, it is not preferable to supply a large amount of nitric acid to the reaction system in the first step.

The reaction product liquid after BTA precipitation can be separated into crude BTA and mother liquor using a conventional separation means such as a filter or a rotary filter.

In addition, according to the method of the present invention, since the amount of yellow compound produced as a by-product in the DXE oxidation reaction in the first step is very small,
Part or all of the mother liquor from which the crude BTA has been separated can be recycled to the first step, the reactor. By taking into account the residual nitric acid contained in this recycled mother liquor and adjusting the amount and concentration of nitric acid supplied to the reactor, the basic unit of nitric acid in the method of the present invention can be reduced, and the recovery rate of crude BTA can be reduced. is significantly improved. However, if the whole mother liquor is recycled many times, a yellow compound as a by-product will accumulate, so it is preferable to recycle 50 to 90% by weight of the mother liquor and discard the rest.

(c) Third step The crude BTA thus obtained is a cream or white powder containing a trace amount of a yellow compound as a by-product. Therefore, in the third step, using water as the recrystallization solvent, crude BTA
is recrystallized to obtain purified BTA. In such recrystallization, for example, industrial water or distilled water with a pH of 6 to 8 is used, and 5 to 1 kg of water is first added to 1 kg of crude BTA.
Heat to 0-100°C to dissolve.

The yellow compound contained in the crude BTA is soluble in the nitric acidic aqueous solution, but not in water. Therefore, this aqueous solution is filtered under a heated state, for example, at 60 to 80° C., to remove the yellow compound. By cooling the aqueous solution after filtration to, for example, 20 to 50°C, BTA is reduced to 0.9 per kg of crude BTA.
Approximately 2 to 0.94 kg is precipitated.

After recrystallization, BTA is separated using conventional separation means such as centrifugation and filtration. Recrystallization may be performed multiple times as necessary, and the separated BTA is dried at about 50 to 200°C to obtain purified BTA.

Note that in recrystallization with water, a certain amount of BTA is dissolved in the mother liquor after recrystallization, and it is unreasonable to discard this, so it is preferable to use this mother liquor repeatedly for recrystallization. However, as water-soluble impurities gradually accumulate,
More preferably, 5 to 25% by weight of the mother liquor is replaced with fresh water and used repeatedly for recrystallization, and the discharged mother liquor is recycled to the reactor.

Effects As described above, the present invention provides (a) oxidizing DXE with nitric acid at a specific concentration and under a specific temperature in the first step to obtain a BTA reaction product liquid with extremely few by-products, and (b) in the second step. In the step, crude BTA is precipitated and separated from this reaction product liquid, and (c) in the third step, the crude BTA is recrystallized using water to obtain purified BTA.

EXAMPLES The present invention will be explained in more detail with reference to Examples below.
The present invention is not limited to such embodiments.

Example 1 300g of 98% by weight sulfuric acid was placed in a 1C flask, and 424g (4 mob) of O-xylene and 90% by weight were added to the dropping funnel.
50 g of acetaldehyde aqueous solution (acetaldehyde 1.
02mo4) was added dropwise. During this time, the inside of the flask was sufficiently stirred and cooled from the outside to maintain the temperature at 15 to 20°C. After completion of the dropwise addition, stirring was continued for 1 hour at 20° C. and then allowed to stand. The reaction solution was separated into two phases, with the upper layer being black. When this upper layer was separated, it weighed 380 g. On the other hand, 200 g of n-hexane was added to the lower layer liquid, and after stirring for 2 minutes, the mixture was allowed to stand for phase separation, and this upper layer liquid was taken and added to the previous upper layer liquid. Next, several cc of 25% by weight aqueous sodium hydroxide solution was added to this and stirred well, resulting in a black liquid.
It turned bright yellow.

When this liquid was distilled, a DXE fraction was distilled out following n-hexane and 0-xylene (5 Torr, approximately 160°C
), and the DXE fraction was 192 g (0,807 mo j).

37 made of 5US-316! Obtained in autoclave]
) XE fraction 120g (0,504mo/) and 3
Take 1350 g of 0% by weight nitric acid (nitric acid 6.43 moβ), raise the temperature while stirring, and heat at 135°C for 1 hour.
The reaction was carried out at 0°C for 3 hours. The pressure was 65 kg/-. The inner hot water was allowed to cool down to 60°C, and the upper valve was gradually opened to release the gas to bring the pressure to normal pressure.The internal liquid was extracted to obtain a yellow-green reaction product liquid.

This reaction product liquid was distilled at about 70° C. under a reduced pressure of 200 Torr to remove water, concentrated until the total liquid amount was 850 g, allowed to cool, and filtered the precipitate.

The precipitate was pale cream-colored crude BTA.

When this crude BTA was vacuum dried and its weight was measured, it was 149.
g, and the purity was 97.3% when analyzed by liquid chromatography.

100 g of this crude BTA and 500 g of water were placed in a beaker and heated to 80°C to dissolve the crude BTA, filtered through a filter paper, and then cooled to room temperature. A small amount of yellow compound was attached to the filter paper. Further, a small amount of BTA powder was added to the filtrate to serve as crystal nuclei to recrystallize BTA, which was filtered to obtain white crystals. When this was vacuum dried, it weighed 92.5'g.
Yes, purity is 99.1% by liquid chromatography
Met.

Obtained white crystal BTA 50g (0.14moβ)
into a flask and add 140 g of acetic anhydride (1,37 moI2
) was added, a distillation column was attached, and the mixture was distilled under nitrogen at normal pressure. When a total of 70 cc of acetic acid and acetic anhydride had been distilled out, the distillation was stopped and the flask was allowed to cool. After the contents of the flask come to room temperature, let it stand for 30 minutes and add the BTDA.
was precipitated and separated by filtration.

The precipitated BTI) A was vacuum dried at 80°C and ITOrr to obtain 4.1.9 g of white BTDA (0.13 mo
β) was obtained.

Example 2 4 g of the DXE fraction (16.8 mm
oj2) and 45 g of 30 wt% nitric acid (nitric acid 214 m
moI! , ) was taken, the temperature was rapidly raised to 160° C. while stirring, and the reaction was allowed to proceed at this temperature for 4 hours. Pressure is internal temperature is 16
When the temperature reached 0℃, it became 18 kg/a (and finally 5
It became 0 kg/-.

Then, when it was cooled to room temperature, the pressure became 35 kg/ctIl, so the gas was gradually released to return to normal pressure, and the reaction product liquid was transferred to a 100 cc flask.

This reaction product liquid was heated and concentrated at about 70° C. at 200 Torr until the liquid volume was reduced to half, cooled, and the precipitate was filtered, which revealed white crude BTA. When this crude BTA was vacuum dried and its weight was measured, it was found to be 3.55 g (9.9 mmo# as BTA), and the purity as determined by liquid chromatography was 98.1%.

12 g of distilled water was added to 3 g of the obtained crude BTA, and the mixture was dissolved at 95° C., and then cooled to recrystallize BTA. The recrystallized white B'TA was filtered and vacuum-dried, and its purity was measured using liquid chromatography.
It was 9.6%.

Comparative Example 1 Using the same autoclave as in Example 2, 4 g of DXE fraction (16.8 m MO7) obtained in the same manner as in Example 1 and 32 g of 422-fold nitric acid (nitric acid 213 m NO/
) and the temperature was rapidly raised to 160°C while stirring. The pressure at this time is 30 kg/ when the internal temperature reaches 160°C.
-, and 85 kg/cat 4 hours after the start of the reaction. Thereafter, crude BTA was separated in the same manner as in Example 2. The obtained crude BTA had a light yellowish brown color, the yield was 2.80 g, and the purity was 7.5%.

However, even when this crude BTA was recrystallized using water as in Example 2, it remained cream-colored and had a low purity of 98.7%. To 2.0 g of BTA obtained by this recrystallization, 6 acetic anhydrides were added.
After distilling a total of 2.5 cc of acetic acid and a portion of acetic anhydride in the same manner as in Example 1, the bottom liquid was cooled to precipitate BTDA. This BTDA was filtered out.
Vacuum drying was performed at 0° C. and 1 Torr.

The obtained BTDA was a pale cream color, not white, and its purity as determined by liquid chromatography was as low as 98.5%.

Comparative Example 2 DXE fraction 4g (16.8m mol) obtained using the same autoclave as Example 2 and the same method as Example 1
and 20% by weight nitric acid 67.5g (nitric acid 214m
mob) was taken, and the temperature was rapidly raised to 160° C. while stirring.

The pressure at this time is 20k when the indoor bath reaches 160℃.
g/, ffl, and 108 kg 6 hours after the start of the reaction.
/cd. Next, the autoclave was allowed to cool, the gas was released to return it to normal pressure, and the contents were transferred to a flask for 2'
It was concentrated to about 25 cc using an OOT o r r. After cooling, the precipitate was filtered and dried to obtain 2.65 g of white crude BTp. The purity of this crude BTA is 97
．． It was 7%. The yield was lower than that in Example 2, and an autoclave having twice the pressure resistance was required, and a large amount of water had to be distilled off in order to precipitate crude BTA.

Comparative Example 3 Using the same autoclave as in Example 2, 4 g of DXE fraction (16,8+ffi mo
i! ) and 45 g of 30% nitric acid (214 m of nitric acid
mob) was taken, and the temperature was rapidly raised to 110° C. while stirring. The pressure at this time became 2 kg/cd when the internal temperature reached 110°C, and when the reaction continued for 10 hours, the pressure rose to 26 kg/call. Then, the autoclave was allowed to cool, gas was released, and the pressure was returned to normal pressure to obtain 3.25 g of crude BTA in the same manner as in Example 2. The obtained crude BTA was pale yellow in color and its purity was 89.3%. When 3.0 g of this crude BTA was added to 12 g of water and heated, an insoluble portion was found, which was filtered at 80° C., and the filtrate was cooled to 5° C. to precipitate BTA, which was filtered and dried. The purified BTA was cream colored and its purity was 98.8%.

It can be seen that when the reaction temperature is low as described above, yellow by-products are produced and the selectivity is deteriorated. In this case, it was found that although purification was possible by recrystallization, the purity of the purified product was inferior to that of Example 2.

Example 3 The experiment was carried out in the same manner as in Example 1, and crude BTA was filtered off. When a part of the filtrate was analyzed, the filtrate contained 3.6% by weight of BTA, 5% by weight of nitric acid, and about 1.0% by weight of BTA.
Contains unknown weight percentage.

695 g of this filtrate, 607 g of 61% by weight nitric acid, and 48 g of distilled water were mixed to obtain BTAl, 9% by weight, and 0.5% unknown.
1350 g of a 30% by weight aqueous nitric acid solution containing % by weight was obtained.

This liquid and 120 g of the DXE fraction were charged into a 3β autoclave, and the temperature was raised while stirring to 125°C for 1 hour.
The mixture was reacted at 0° C. for 3 hours and allowed to cool.

Next, the gas was released and the contents were transferred to a flask for 200 ml.
Distill under reduced pressure at Torr until the liquid volume reaches about 850g? Ii! The mixture was allowed to cool, and the precipitate was filtered to obtain crude BTA.

The obtained crude BTA had a light cream color and weighed 173 g when vacuum dried. Analysis by liquid chromatography showed that the purity was 97.1%, which was almost the same as in Example 1.

Therefore, the yield increased by about 24 g compared to Example 1.

80 g of this crude BTA and 400 g of water were placed in a beaker, heated to 80°C, dissolved, and cooled to 50°C.
The mixture was filtered through a filter paper and further cooled to 25°C to recrystallize BTA. The precipitate was filtered and dried under vacuum to yield 74.5 g, with a purity of 99.5 g by liquid chromatography. ．． 1% white B
I got a TA. Next, take 300 g of the filtrate from this filtration, add 100 g of water and 80 g of crude BTA, heat and dissolve, filter at 50°C, cool and recrystallize, separate by filtration and dry. A white BTA with a purity of 99.0% by chromatography was obtained.

Effects of the Invention As described above, according to the present invention, high-purity white BTA with a high reaction rate and few by-products can be obtained, and the mother liquor obtained in the second step and/or the third step can be obtained. If recycled, the process can be run extremely economically.

Claims (1)

[Claims] 1. A method for producing benzophenone tetracarboxylic acid, characterized by including the following steps: (a) bis(dimethylphenyl)ethane at a concentration of 25 to
The first step is to carry out an oxidation reaction using 40% by weight of nitric acid at a temperature of 120 to 170°C. (b) A second step of concentrating or cooling the reaction product liquid, or cooling after concentration to precipitate and separate crude benzophenonetetracarboxylic acid. (c) A third step of recrystallizing crude benzophenonetetracarboxylic acid using water as a recrystallization solvent. 2. The method for producing benzophenone tetracarboxylic acid according to claim 1, wherein part or all of the mother liquor after precipitating and separating the crude benzophenone tetracarboxylic acid is recycled to the first step. 3. The method for producing benzophenonetetracarboxylic acid according to claim 1 or 2, wherein part or all of the mother liquor after recrystallizing the crude benzophenonetetracarboxylic acid is recycled to the third step as a recrystallization solvent. .